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//ismaxphase Determine whether filter is maximum phase or not
// Description : It determines whether the given system function is maximum phase system or not . Maximum phase system means all zeros of transfer function will be outside the unit circle in z-plane also poles mustbe within unit circle for stability and causality
//Syntax
//flag = ismaxphase(b,a)
//flag = ismaxphase(sos)
//flag = ismaxphase(...,tol)
// b and a are the vectors containing numerator and denumerator coefficients respectively
//tol, tolerance is used to determine when two numbers are close enough to be considered equal.
//Example : of maximum phase system
//flag = ismaxphase([1 -5 6],1)
//Output
// flag =
//
// 1.
//Author: Parthasarathi Panda
//parthasarathipanda314@gmail.com
function ismax=ismaxphase(varargin)
[nargout,nargin]=argn();
if (nargin==2) then
a=varargin(1);
b=varargin(2);
if type(a)~=1 | type(b)~=1 then
error('check input type');
end
v=size(a);
if length(v)>2 then
error('check input dimension');
end
v=size(b);
if length(v)>2 then
error('check input dimension');
end
[n,k]=size(a);
if k==1 then
a=a';
elseif n~=1 then
error('check input dimension');
end
[n,k]=size(b);
if k==1 then
b=b';
k=n;
elseif n~=1 then
error('check input dimension');
end
elseif (nargin==1) then
sos=varargin(1);
if type(sos)~=1 then
error('check input dimension');
end
v=size(sos);
if length(v)>2 then
error('check input dimension');
end
if v(2)~=6 then
error('no. of columns must be 6');
end
a=1;b=1;
for i=[1:v(1)]
a=convol(a,sos(1:3));
b=convol(b,sos(4:6));
end
else
error('no. of inputs not matching');
end
poly_a=inv_coeff(a);
poly_b=inv_coeff(b);
z=inv_coeff([1,0]);
gc=gcd([poly_a,poly_b]);
[r,den]=pdiv(poly_b,gc);
[r,num]=pdiv(poly_a,gc);
maxpole=max(abs(roots(den)));
minzero=min(abs(roots(num)));
if length(b)==1 then
if length(a)==1 then
ismax=1;
elseif minzero>1 then
ismax=0;
else
ismax=1;
end
elseif maxpole>1 then
if length(a)==1 then
ismax=0;
elseif minzero>1 then
ismax=0;
else
ismax=1;
end
else
ismax=0;
end
endfunction
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